The present invention relates to a hydrodynamic start-off element for a drive train of a motor vehicle for converting an input rotary speed and input torque of a drive motor into an output rotary speed and output torque.
Known hydrodynamic start-off elements are, for instance, hydrodynamic torque converters. A hydrodynamic torque converter is the standard start-off element for conventional automatic transmissions. It does not only convert the rotary speed (clutch) but also a rotary speed/torque (transmission). The individual components of the hydrodynamic torque converter are hydrodynamic devices that form a closed hydrodynamic circuit. An impeller converts mechanical energy introduced by a drive shaft into the hydraulic energy of a fluid and a turbine then reconverts the hydrodynamic energy into mechanical energy, which may then be taken off on an output shaft (minus the losses that have occurred). In addition to its two main components, the impeller and the turbine, a hydrodynamic clutch in general includes a stator for converting torque (for instance what is known as a Föttinger clutch or a Trilok converter).
In the known hydrodynamic start-off elements, the impeller is usually part of a converter housing. As a consequence, a drive-side moment of inertia of such hydrodynamic start-off elements is comparatively high, a fact which has an unfavorable effect on the driving dynamics on the drive side, i.e., on an acceleration and deceleration of the hydrodynamic start-off element. In contrast, the moment of inertia on the power take-off side is comparatively low in the known hydrodynamic start-off elements. This in turn causes the characteristic mode of the natural frequency of the drive train to be at unfavorably high rotary speeds.